Project Summary Parkinson's disease (PD) is a common, progressive and disabling condition with no cure. Accumulating evidence from human genetics, cell biology and animal model studies suggest that ?-synuclein is a key protein, as it misfolds and forms fibrils that can propagate across neurons, a phenomenon that can account for the progressive nature of the disease and the emergence of additional disturbing symptoms including dementia over time. A strong driver of pathological ?-synuclein aggregation is its concentration in the brain, as individuals with multiplication of the SNCA gene locus develop early onset PD and dementia with a gene dosage effect. Thus, reducing ?-synuclein protein expression is a plausible disease modifying strategy for PD. This approach targets the root pathogenetic mechanism of the disease and has the potential to mitigate downstream cascades of pathologic events and slow down neurodegeneration. Using a series of innovative chemical and cell biologic approaches, we have identified small molecules with diverse chemotypes that selectively bind to a regulatory element in the SNCA 5' untranslated region, repress translation, and reduce steady state ?-synuclein protein levels leading to cytoprotection. Transcriptome- and proteome-wide studies show that the lead small molecule, named Synucleozid, is more selective than an SCNA-directed siRNA. Using Synucleozid as a prototype, we have identified additional diverse scaffolds that reduce ?-synuclein protein levels and have favorable properties for blood-brain barrier penetrance, as defined by Lipinksi's Rule of 5, properties of CNS drugs, and CNS-MPO calculations. In this Blueprint Neurotherapeutics project, we will optimize these compounds using a highly tailored systematic drug discovery and development funnel. In Aim 1 (UG3), we will take a target validation, selectivity, and in vitro DMPK-driven approach to identify the optimal scaffolds to advance to early stage medicinal chemistry studies to define structure-activity and structure-property relationships. Using iterative rounds of optimization, compounds will be evaluated using a comprehensive in vitro and cell-based screening funnel in preparation for entering the UH3 phase. We will also complete transcriptome- and proteome-wide selectivity studies in PD patient-derived cells, Subsequent aims (UH3) will include in vivo proof of mechanism, therapeutic index assessment, and IND-enabling studies, all culminating in a Phase 1 clinical trial.